Many metals need to be surfaced in order to be applied to various purposes of use. Numerous surfacing materials and methods for arranging these are known. A few examples of these that can be mentioned include surfacing metals with other metals, with rubber-based substances, and with paints using various painting methods. In addition to the above, methods and surfacing materials used in them are also known, which attempt to exploit the electrochemical properties between the surface to be treated and the surfacing material.
Though most of the metal surfacing materials and the methods based on them will indeed achieve the desired end result, the surfacing is then also expensive. Factors associated with the size of the pieces to be surfaced often also limit the use of these methods. In many cases, the temperature of the piece to be surfaced must be brought to such a high level as to even make the surfacing impossible in practice.
Many methods for surfacing a metal with a metal are only suitable for being carried out in permanent plants, thus limiting, for example, the size of the pieces being treated and increasing transport costs. In addition, in certain cases some of the metal surfacing materials may lead to problems, for example, in processes related to the recycling of the metal. In many cases, the use of the various rubber and plastic surfacings is limited while they are often also expensive.
The most widely used metal surfacings are the various paints that are spread using very many different techniques. There are also many problematic aspects relating to painting. The difficulty of getting the paint layer into cramped and complex structures must be regarded as one of the most important of these. In such cases, if the paint layer is either too thin, or is entirely lacking in even small parts of the structure, corrosion damage can start and lead to structural damage. Another very common problem is the paint being knocked or scratched off the surface of the metal, which will also cause corrosion damage to start.
For the above reasons, the paint layer must often be repaired or even entirely renewed, sometimes at very short intervals. The removal of the previous paint layer, the repair of possible corrosion damage, and the spreading of new layer of paint demands time and leads to expenses.
Further, when using all of the aforementioned methods, cleaning, in which dirt and grease are removed, must be carried out on the metal surface prior to the surfacing treatment. If there is, for example, mill scale on the surface, pickling treatment is then becomes practically indispensable.
EP patent publication 0 193 419 (Fairchild Semiconductor Corporation) discloses vapour surfacing that is carried out at low pressure. The surfacing material used in the method is brought to the process in a solid state. The pressure and flow of the gas flow to the surfacing chamber are regulated with the aid of valves, nozzles, and a special cold condensed system arranged in a loop of the feed line, as well as a vacuum booster pump. However, the disclosed method and apparatus are difficult to arrange, for example, as a mobile unit and particularly the treatment of large surfacing objects demands large chamber structures. In addition, the vaporization apparatus must be arranged in a relatively large furnace, which must be kept at a higher temperature than that of the actual vaporization apparatus.